1. Field of the Invention
The invention relates to a battery pack, and more particularly, to a circuit board of a battery pack in which cracks are prevented from being generated in the FPCBs when the FPCBs are bent.
2. Description of the Prior Art
A typical battery pack used in portable electronic apparatuses includes a plurality of bare cells, a protective circuit module (PCM) in which a protective circuit for controlling the charge and discharge of the bare cells is formed, and a terminal line for electrically connecting the bare cells and the protective circuit to each other. The bare cells, the PCM, and the terminal line can be accommodated in a predetermined case.
In the above-described battery pack, the plurality of bare cells are connected to each other in series or in parallel using a tab member to have predetermined voltage and current. The terminal line is connected to the terminal of one cell among the bare cells which are connected to each other in series or in parallel. For example, a conductive tab or wire is connected to the PCM having the protective circuit for controlling the charge, discharge, and the operation of the plurality of bare cells, and the bare cells and the PCM are electrically connected to each other using solder.
The protective circuit connected to the bare cells, and a connector attached to an external electronic apparatus, are electrically connected to each other by electricity that passes through the PCM. Also, protective devices such as thermistors, thermal fuses, and positive temperature coefficient devices can be connected to the PCM.
As described above, a common battery pack includes a plurality of bare cell batteries in a case. A circuit board on which a connector and electronic components are mounted in a circuit pattern, such as a protective circuit, is accommodated into the case. The circuit board is for transmitting and receiving an electrical signal between the bare cell battery and the outside. Accordingly, as electronic products become smaller and more complicated, in order to accommodate the circuit board into the battery pack, whose case is also smaller, it is necessary to effectively use the internal space of the case. One useful method is to use a circuit board with a built in bend.
FIG. 1 is a schematic plan view illustrating the circuit board of a conventional battery pack. As illustrated in FIG. 1, the circuit board 10 of the conventional battery pack includes a first board 11 on which a predetermined circuit pattern is formed, a second board 12 on which a predetermined circuit pattern is formed, and a third board 20 for electrically connecting the first board 11 and the second board 12 to each other.
The first and second boards 11,12 of the circuit board 10 are physically connected to each other with a bending line L interposed. In a state where one side of the first board 11 and one side of the third board 20 are connected to each other, and one side of the second board 12 and the other side of the third board 20 are connected to each other, the first board 11 and the second board 12 are electrically connected to each other. The above-described third board 20 is a flexible printed circuit board (FPCB), which constitutes a circuit pattern and can be bent. Therefore, in order to accommodate the circuit board 10 into the limited space of the case, when the first board 11 and the second board 12 are oriented at a predetermined angle through the bending line L to be physically separated from each other, the third board 20 electrically connects the first board 11 and the second board 12 to each other.
The structure of the circuit board 10 will be described in detail. Predetermined patterns are formed on one surface or both surfaces of each of the first and second boards 11, 12 and electronic components D such as a connector, a semiconductor chip, and a resistor are mounted on the surfaces of the first board 11 and the second board 12. The electronic components D are electrically connected to wiring line patterns 16,17. Terminals 18 connected to the wiring line patterns 16 are formed in the parts where one side of the first board 11 and one side of the third board 20 are to be connected to each other. Terminals 19 connected to the wiring line patterns 17 are formed in the parts where one side of the second board 12 and the other side of the third board 20 are connected to each other. The terminals 18 and 19 are electrically connected, using solder, to the circuit pattern 21 (hereinafter, referred to as a pad) of the third board 20. Reference numeral 22 denotes a soldered connection. The first and second boards 11,12 connected to each other through the pad 21 of the third board 20 are electrically integrated with each other to function as one board. The first board 11 and the second board 12 of the circuit board 10 are bent along the bending line L such that they are separated from each other so that the circuit board 10 may fit in the limited space left with the battery in the case (not shown). Although the first board 11 and the second board 12 are physically separated from each other, they are electrically connected to each other through the third board 20 so that the electrical power and the electrical signal of the battery are exchanged between the battery (not shown) and the external apparatus through the connector and the electronic components of the circuit board 10.
FIG. 2 is a schematic sectional view illustrating that the circuit board of the prior art.
In order to connect one side of the first board 11 and one side of the third board 20 to each other and to connect one side of the second board 12 and the other side of the third board 20 to each other, a conventional hot bar method is used which is well known in the art. In the method, first, solder such as SnPb is printed in the region where one side of the first board 11 and one side of the third board 20 are to be connected to each other and in the region where one side of the second board 12 and the other side of the third board 20 are to be connected to each other. The third board 20 to which the solder is printed is pressed by a hot bar to form the soldered connections. Therefore, one side of the first board 11 and one side of the third board 20 are connected to each other, and one side of the second board 12 and the other side of the third board 20 are connected to each other through the solder 22.
When the circuit board 10 having such a structure is bent along the bending line L of FIG. 1, cracks can be generated in the third board 20 in the solder 22. In the situation where the solder is soldered by the hot bar, and the thickness of the solder 22 is not uniform, an external shock, such as when the board is bent, may adversely affect the solder 22. In particular, the parts that are not uniformly pressed by the hot bar slightly protrude and can be affected by the force generated by the circuit board 10 being bent, and cracks can be generated in the third board 20. The cracks generated in the third board 20 can prevent the first board 11 and the second board 12, that are physically separated from each other by the bending of the circuit board 10, from being electrically connected to each other. Therefore, the cracks may not allow the exchange of the electrical signal between the battery and the external apparatus.
In order to solve the above problem, the circuit board is manufactured in a flame lead method in which a flame leader component is used and built in the case of the battery instead of the low priced FPCBs. Cracks are rarely generated in the circuit board manufactured using the flame lead method. However, since the flame leader component is expensive, and process equipment for the reflow process that is performed in the flame lead method is also expensive, the flame lead method is ineffective in terms of expense. Therefore, it is necessary to use the low priced FPCBs without generating the cracks when the circuit board is bent.